The purposes of this study are to investigate bacterial factors of importance in the pathogenesis of infections caused by Gram-negative bacilli and means of enhancing immunity to such infections in man. Prior studies have demonstrated that both active and passive immunization of experimental animals, using an antigen shared by almost all enterobacteria (Re determinant of R strains of S. minnesota), affords significant protection against challenge with heterologous Gram- negative bacilli. Similarly, patients with high titers of antibody to Re experienced shock and a fatal outcome during the course of Gram- negative bacteremia only one-third as often as patients with low titers of antibody to Re. This apparent protective effect of antibody to Re was independent of any effect of O antibody. Studies of the immunizing ability and toxic effects of killed Re mutants of S. minnesota, Boivin and Westphal endotoxins, endotoxins detoxified by alkali, acetylation, etc., and a ribosomal vaccine will be undertaken in experimental animals. Once a non-toxic, satisfactorily immunogenic vaccine preparation has been developed, further studies of immunogenicity and toxicity will be undertaken in volunteers. After satisfactory completion of volunteer studies, field trials to evaluate the efficacy of immunization will be undertaken among patients on a Urology Service to determine the vaccine's efficacy in reducing the frequency and ameliorating the severity of Gram-negative bacteremia. Other studies will relate the quantity of K antigen in E. coli, circulating endotoxin, bradykinin alterations, and complement levels to the severity of Gram- negative bacteremia.